The present invention relates generally to semiconductor devices, and, more particularly, to a semiconductor device having a novel electrode structure and a method for manufacturing the same.
Generally, the gate electrode of a metal oxide semiconductor (MOS) transistor is made of polysilicon doped with impurities. Such a polysilicon gate electrode provides a significant advantage over competing alternatives, such as metal gate electrodes. Namely, the process for manufacturing polysilicon gate electrodes can be more stably and tightly controlled than the process for manufacturing metal gate electrodes. However, polysilicon gate electrodes have a significant disadvantage, namely, the sheet resistance thereof is higher than that of metal gate electrodes. More particularly, the sheet resistance of polysilicon gate electrodes is nearly 1,000 .mu..OMEGA./, which results in decreased signal transmission speed and increased power consumption of the MOS transistor and associated semiconductor device. These disadvantages of polysilicon gate electrodes have become a more important factor as the level of integration (i.e., integration density) of semiconductor devices has increased. Thus, such drawbacks and shortcomings of polysilicon gate electrodes have imposed limitations on device capacity and reliability.
On the other hand, while metal gate electrodes exhibit significantly lower sheet resistance than polysilicon gate electrodes, they present other problems. Most importantly, during the fabrication of a semiconductor device, process steps which are performed subsequent to the formation of the metal gate electrode cause the metal to diffuse into and/or precipitate onto underlying layers of the device, thereby greatly degrading or destoying the operational characteristics of the device.
Based on the above, it can be appreciated that there presently exists a need in the semiconductor art for a semiconductor device having a gate electrode structure, which overcomes the above-described drawbacks and shortcomings of presently available gate electrode structures. The present invention fulfills this need.